1. Field of the Invention
The present invention relates to the synthesis of silver nanoparticles, and particularly to synthesis of highly dispersed silver nanoparticles recovered from photographic and X-ray medical film waste.
2. Description of the Related Art
Because of their unique properties (e.g., size and shape depending upon optical, electrical, and magnetic properties), silver nanoparticles can be useful in antimicrobial applications, biosensor materials, composite fibers, cryogenic superconducting materials, cosmetic products, and electronic components. Several physical and chemical methods have been used for synthesizing and stabilizing silver nanoparticles. Conventional methods for producing silver nanoparticles from silver chloride, however, typically require use of toxic reducing agents.
Silver is the reflective coating of choice for solar reflectors, and X-ray films used in medicine and photographic plates. Around 18-20% of the world's silver needs are supplied by recycling photographic waste. It has been reported that 25% of the world's silver needs are supplied by recycling, out of which 75% is obtained. Thus, X-ray films can serve as a secondary source for recycled silver.
Various methods have been utilized in the recovery of silver from X-ray films, which include adsorption of silver from synthetic photographic and spent fix solutions on granulated activated carbon in a batch process; industrial enzymatic process for the recovery of silver and poly(ethylene terephthalate) (PET) from used lithe film for printing; spent fixing bath; using a constructed pilot reactor with a protease from an alkalophile; and recovery of silver from X-ray film processing effluents by precipitation. Silver recovered from X-ray films by dissolving the silver compounds with concentrated nitric acid showed that a very high quantity of silver can be recovered. Silver has also been recovered from photographic processing solution by replacing the silver with another metal such as zinc by electrolysis or by chemical precipitation with sulphide. Silver is then recovered from silver residue. However, stripping the gelatin-silver layer by conventional methods can cause environmental hazards, are time consuming, or are very expensive.
Thus, a method of synthesizing silver nanoparticles using film waste solving the aforementioned problems is desired.